Devices for cooling the outboard portions of inboard-outboard marine power drive systems, commonly called I-O, stern drive, or outdrive systems are well known. See, for example, U.S. Pat. No. 4,371,351 issued Feb. 1, 1983 to Gordon Tousey, which describes problems often encountered with these units due to overheating of gears and lubricants. Thermal cycling of the housing also creates problems. The patent also describes apparatus for cooling the outboard systems by using the ram effect to scoop water from the supporting medium, conduct it up and spray it over the stern drive unit.
Cooling systems of this kind have been found to be effective in reducing the operating temperatures of the stern drive units, and thereby significantly reducing the failure rate and improving durability. The effectiveness of the systems is especially beneficial in high performance and racing boats, and is also advantageous in units that operate under less severe stress.
In modern installations of this kind the cooling systems are mounted on the stern drive units, avoiding the distaste most boat owners have toward mounting the systems on the transoms of their boats, simplifying the installation, and generally making for a neat and unobtrusive appearance. Vertical holes are drilled in the anti-cavitation plates of the stern drive, one hole for each of the water intake tubes in the cooling system, the holes being sized to fit the tube, or tubes closely. The tube, or tubes are then inserted through the holes from above, extending about three inches or so below the plates and into the propeller stream.
The tubes are open ended, cut at about a 450 angle and positioned with their open, oval faces directed forwardly.
The opposite, upper end of the tube, or tubes is then secured, usually by a single fastener, to the body of the drive unit near its top. Outlet openings, called dump ports, are cut in the intake tube at strategic points along its length to direct water toward and upon the body of the unit.
This is the arrangement of concern here. A problem presents itself especially in so-called high performance and racing boats when they are operated at high stress and their drivers are trying to maximize speed. Under these conditions the cooling systems often fail to deliver the expected cooling water; at times when maximum cooling is desired and needed the systems reduce their efficacy and often fail to deliver any water at all.